The ESP (Earth Systems Project) is also an event held during IESO2022, which requests international groups of students to investigate one of the four topics on Earth System Phenomena and make presentation to the International Jury. The topic I selected was Climate Change’s Effects on Natural Hazards (one of the four topics provided by the committee) and then I was assigined to a group where students also chose this topic. My teammates were from Japan, South Korea, Bangladesh, Indonesia, Australia and UAE, and we chose to work on climate change’s impact on tropical cyclones specifically.
Myself Ziyan Fang and team 18 group members will be presenting our Earth science project. For our Earth systems project, we investigated how tropical storms are connected to phenomena such as climate change and the El Niño Southern Oscillation. We also looked at how this affects Earth’s systems.
Our topic was to investigate the impacts of climate change on natural hazards. For something to be a natural hazard, it has to be a natural event with potential negative impacts on society. A very large number of phenomena fit these criteria, and are not just limited to earthquakes, tropical cyclones, volcanic eruptions, sandstorms, floods and drought, but each one has complex connections to Earth’s systems and to climate change. For this reason, we decided to focus just on one topic for our project and hope to cover it more in depth. We chose to investigate the natural hazard of tropical storms, which are known as tropical cyclones, hurricanes or typhoons depending on where they originate.
Information about Climate Change
To understand how climate change would influence tropical cyclones, we first need to get some basic information about climate change. Our climate system is controlled by plenty of mechanisms, including plate position, Milankovitch cycle, thermohaline circulation, solar activity, volcanic activity, greenhouse effect, ect., among which the first five are mainly long-term or mid-term mechanisms, whilst the final one, greenhouse effect, is the one dominating the change of climate in the recent one hundred years. It refers to the effect that some gas molecules containing two or more atoms of different elements would have net change in the distribution of their electrical charges when they vibrate, and hence can absorb and emit the infrared radiation and subsequently warm the earth’s surface.
From the chart on the left we could see that the gases that contribute most to the greenhouse effect and climate change re CO2, CH4 and NO2, whose concentration ratios have largely increased since the industrial revolution.
In fact, the current climate change is also supported by evidence from all aspects. According to IPCC AR5, our earth is undergoing a series of phenomena including increased surface temperature, fastened water circulation, melting glaciers, decreased seawater PH, and so on, which disturbs our original climate patterns and alters the intensity and distribution of natural disasters, of which tropical cyclones would be a typical one that is closely associated with human society. So, specifically, how will climate change affect tropical cyclones and lead to further impacts on different spheres in the earth system? To answer this question, we must first get some information about tropical cyclones.
Information about Tropical Cyclone
A tropical cyclone is a cloud-rotating storm and a warm low pressure system. Tropical cyclones rotate due to the Coriolis force in the ocean where the temperature of the ocean water is at least 27°C. Tropical cyclones form in warm regions a short distance from the equator.
Let me explain how tropical cyclones form. First, the seawater is heated, and the water evaporates to form water vapour. In the tropics, where temperatures are higher, the atmosphere can contain more water vapour. Next, the evaporated water vapour collects and rises in a spinning motion. After that, it is cooled by the cold upper air and clouds form. As the rising air currents send more and more water vapour into the air, the clouds become warmer and warmer to form cumulonimbus clouds. At this time, a large amount of vapour becomes water, which releases a large amount of latent heat. This heat warms the air around it, making the updraft stronger and the atmospheric pressure lower. This repetition produces tropical cyclones.
Climate change’s impact on tropical cyclone
Frequency: There is evidence that the frequency of tropical cyclones has decreased since industrialisation. There has been a 13% decrease in tropical cyclone frequency between the 1850-1900 period and the 1900-2012 period (Thompson, 2022). The graphs on the slide demonstrate a negative trend for the frequency. A possible reason for this is that climate change can weaken the circulation of Hadley and Walker cells. This is hypothesised to produce less favourable conditions for the formation of tropical cyclones, reducing the number of tropical cyclones that have formed. Another potential reason is the increase in maximum humidity of air due to temperature rise. To form a cyclone near saturation from the surface to a height of 5–7 km is a necessary condition for tropical cyclone development. And due to the increase in absolute humidity it is harder to reach the near saturation level within the specific height and we are seeing a decreasing trend in the numbers of cyclones forming.
Intensity: It is much more agreed that climate change increases the intensity of tropical storms. This may be because an increased temperature leads to increased evaporation and thus more warm air rising and more moisture. When the tropical cyclone has more moisture it can intensify its impact through increased precipitation. The plots project a lower frequency of tropical cyclones in all regions, but an increased intensity and rain rate in all regions. This projection is for an increase in global temperature of 2 degrees celsius.
Location: As global temperatures increase, the temperatures required to form tropical cyclones move closer to the poles. Therefore, the latitude of maximum intensity is getting closer to the poles. Between 1982 and 2009, the average location of Northern hemisphere tropical storms has moved north by 53km, and Southern hemisphere tropical storms have moved south by 60km. Moreover, the change in vertical wind shear change is causing rapid intensification at some regions.
Tropical cyclones’ effect to El nino
As you know, the ENSO, El Niño-Southern Oscillation is the interaction of hydrosphere and atmosphere in the southern pacific ocean. El Niño and La Niña are the warm and cool phases of a recurring climate pattern across the tropical Pacific. The pattern shifts back and forth irregularly every two to seven years, and each phase triggers predictable disruptions of temperature, precipitation. These changes hugely interact with the earth systems’ tendency.
How can the tropical cyclones modulate ENSO? There are two main effects intensify the El nino.
These are the schematic diagrams of the modulation of running 3-month mean SST intensity for the Niño 3.4 region by tropical cyclones over the western North Pacific.
The light blue circle, Walker circulation is weakened by the direct effect of asymmetrically anomalous westerlies within light blue thick arrows related with TCs at lower tropospheric levels and by the indirect effect of the Hadley-like circulation (red circle) over the tropical western Pacific. Moreover, red dashed curve shows TCs can shallow the thermocline in the tropical western Pacific (pink curve indicates the thermocline without TCs and blue solid line the climatological thermocline). Enhanced eastward-propagating equatorial Kelvin waves (red wavy arrow, pink wavy arrow indicates the Kelvin wave without TCs carries warm water eastward, further deepening the thermocline in the tropical eastern Pacific, thereby reducing the gradient of the zonal thermocline in the equatorial Pacific Ocean.
In the picture, you can see the zonal eastern wind in the southern pacific ocean enhancement during the main duration of the cyclone. Changes of ENSO due to tropical cyclones could induce Unprecedented abnormal weather.
Interactions of spheres in a tropical cyclone
So, let’s talk about tropical cyclone affect our atmosphere.
A tropical cyclone is like a giant, atmospheric heat engine. The moisture from the warm ocean acts as its fuel, generating huge amounts of energy as clouds form.
The rotating thunderstorms form spiral rainbands around the eye of the cyclone where the strongest winds and heaviest rain are found, known as the eye wall, transporting heat 15 km or higher into the atmosphere. The drier cooler air at the top of the atmosphere becomes the exhaust gas of the heat engine.
This picture shows increasing wind speed and precipitation around a tropical cyclone. This data is from hurricane Katrina that occurred in August 2005. As you can see, the increased precipitation followed the track of the cyclone. And you can see also, there is increasing wind speed around the cyclone. So, what is the effect?
Strong winds in tropical cyclones lead to large waves on the sea called storm surges. So, What is a storm surge actually? Storm surge is an abnormal rise in sea level above the normal tide levels, and can be thought of as the change in the water level due to the presence of a storm. The height of the storm surge varies depending on how strong the cyclone is. The faster the wind speed, the higher the storm surge that is generated. We got the Katrina TC’s wind speed is SS5, which can generate storm surge up to 24 feet.
When storm surges move to the coast, they erode the Earth’s crust and sediments. This can change the topography of the coast. As you can see in this picture, the coastline pushes further into the land. Plus, Climate change causes sea level rise, making storm surges reach even higher in relation to land, making storm surge even more destructive. If the tc enters even farther to land (Hurricane Maria), it causes many massive landslides as you can see in the picture.
Tropical cyclones damage biological organisms, especially near the coast. Storm surges can cause flooding for a few days. Populations of organisms that can’t defend themselves and adapt through this change will be decreased. This causes secondary succession, where organisms that can adapt to tropical cyclone conditions become more abundant. This phenomenon changes the ecology of the area.
Tropical cyclones and storm surges also cause many human fatalities, especially near the coast. We took data of fatalities caused by the dangerous tropical cyclone bhola. The human fatalities are 300k-500k. Imagine, with this climate change causing the increased intensity of tropical cyclones, how many more lives will fall if we don’t prevent climate change.
Conclusion
Tropical cyclones are a natural hazard with the ability to cause widespread damage. The growing phenomenon of climate change amplifies these devastating effects by increasing their intensity, but not their frequency. This has follow-on consequences for all of earth’s systems, showing that Earth’s spheres are all connected. Tropical cyclones cause and are driven by atmospheric phenomena such as wind and cloud and storm formation. They interact with the hydrosphere because they are formed from the evaporation from water bodies, and cause precipitation. Tropical storms and their storm surges interact with the geosphere by eroding sediments from the coastline, possibly causing landslides. They also interact with the biosphere by damaging organism populations, including human populations, and can alter the ecology of an area. The Earth is an interconnected system, and this investigation of tropical storms has found links to climate change and all four of Earth’s systems. Thank you.
Original link: https://fiona-f-ang.github.io/index.html
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